The geologic overview map shows a dramatic boundary along the Front Range between the very old granite and metamorphic rocks of the Rocky Mountain block, uplifted on the west side of a fault zone and the Great Plains block on the east. In an area of a few square miles, however, the small remnant of early sedimentary rocks at Manitou Springs, some of the oldest sedimentary rocks in the region are preserved on top of the Pikes Peak granite and metamorphic rocks in the upthrown Rocky Mountain block, west of the great bounding faults of the Front Range. Almost all of these sedimentary rocks have been eroded away over millions of years from the remaining area of the Rocky Mountain block.

The Manitou Limestone, and parts of the underlying sandstone and weathered granite, and overlying dolomite and limestone beds, constitute the Manitou Springs artesian aquifer, and the Fountain Formation serves as a sequence of low-permeability confining beds above it. The aquifer is the result of the dissolution of carbonate rocks by slightly acidic rainwater that seeps into the ground through fractures and joints. Once underground, the water slowly dissolves the soluble rocks into subterranean passages, caverns and caves. The result of this process is defined as a karst landscape. The mostly-dormant part of the Manitou Springs aquifer, now above the water table, is a cave system located north of the city called “Cave of the Winds”.

Carbonated Mineral Water

One of the most intriguing aspects of Manitou Springs is the carbon dioxide content of the gas emanating at the springs. The gas, is composed almost entirely of carbon dioxide, a characteristic not typical of low-temperature aquifers. By volume, the carbon dioxide content of gas at the springs ranges up to nearly 99 percent. In contrast, shallow groundwater containing dissolved gas originating from the atmosphere or soil typically has less than 1 percent by volume. Due to the purity of the gas composition, helium isotope evidence suggests that a significant portion of the carbon dioxide likely originates at depth from Earth’s outer mantle and migrates to the Manitou Springs aquifer along the Rampart Range and Ute Pass Fault Zones.

Below is a graphic depicting the geologic stratigraphy of the area that tells the story of the type of environment that deposited each sedimentary layer.

Images correlate with strat column on left.(click for more info) ←Surface gravels

Fountain Formation

Thick alluvial fan deposits of the overlying part of the Fountain Formation were the result of the Ancestral Rockies uplift. The uplift arose quickly from the shallow sea causing massive erosion that carried coarse sediment into the surrounding basins. The entire formation is up to 4,050 feet in thickness dating to 299-318 millions of years ago.

Glen Eyrie Member of Fountain Formation

A transitional era defines the Glen Eryie member from a marine environment to terrestrial. The sandstone beds were deposited by small fluvial channels transporting and depositing sand from dry areas into receding shallow seas. The Glen Eryie is considered an aquaclude, meaning a confining layer.

Leadville Formation

A Hardscrabble member of the Leadville Limestone dating to the Mississippian period 318-360 million of years ago. During this period, a widespread tropical shallow limy sea covered most of western North America precipitating vast carbonate deposits across Colorado. The shallow limy seas were conducive for lime-secreting marine organisms such as brachiopods, corals and echinoderms. The thickness of the formation in the Manitou Springs area is approximately 100 feet.

Williams Canyon Formation

The Williams Canyon Limestone is approximately 30 feet thick sitting unconformably over the Manitou Formation, meaning the underlying Manitou experienced an erosional period before the Williams Canyon Formation was deposited. Williams Canyon Limestone is dated from from the late Devonian period 360-416 million of years ago described as a depositional cycle situated at the edge of a shallow sea that inundated south-central Colorado from the west. Furthermore, part of the formation contains rounded and frosted quartz grains suggesting wind-blown sand deposits which explains the formation’s lack of fossils.

Manitou Formation

A Limestone deposited between 444-488 million of years ago during the Ordovician period by warm, shallow limy seas when the North America continent was located on or near the equator. It was a time where plants and animals gained a terrestrial foothold. The aquifer that supplies the mineral springs is formed principally by fractures, and fractures that have been enlarged by solution of carbonate rocks, in the upper part of the sequence of limestone beds of the Manitou Formation, but also in overlying limestone beds of the Devonian-age Williams Canyon Formation and Mississippian-age Leadville Formation. The aquifer also appears to include sandstones of the Sawatch Sandstone underlying the Manitou, and weathered Pikes Peak granite beneath the Sawatch.

Sawatch Formation

The Sawatch Sandstone was deposited during the late Cambrian period dating to 488-542 million of years ago. The formation overlies the Pikes Peak Granite as a nonconformity in the area of Manitou Springs, the situation of a sedimentary formation overlain upon an intrusive rock (two different types of rock) and a gap in the geologic time record of over a half a million years. During the Cambrian period, Colorado was inundated by shallow seas from the west depositing sediment on top of the eroded Precambrian Pikes Peak Granite. A good example of the contact can be viewed along the lower section of the El Paso County Open Space trail to Rainbow Falls on the west end of Manitou.

Pikes Peak Granite

Pikes Peak Granite is part of the Pikes Peak Batholith, Formed between 1.02-1.08 billion of years ago deep underground by hot magma produced from Earth’s core and a later the source of volcanic eruptions. The batholith remained deep underground cooling for millions of years reaching the surface as granite during the late Mississippian to early Permian period, 270-320 million of years ago. This was the time of mountain building events that created the Ancestral Rocky Mountains. The thickness of the Pikes Peak granite is unknown.